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Biomedical subjects

T Braulke

Publications and source records attributed to T Braulke.

At least 19 recordsLinked to original sources

Brain-specific interaction of a 91-kDa membrane-bound protein with the cytoplasmic tail of the 300-kDa mannose 6-phosphate receptor.

The cytoplasmic tail of the 300 kDa mannose 6-phosphate receptor (MPR 300-CT) is thought to play an important role in sorting and targeting of lysosomal enzymes and the insulin-like growth factor II along the biosynthetic and endocytic pathway. In this study a brain specific 91 kDa protein and a 35 kDa protein salt-washed from membranes (referred as TIP 91-M and TIP 35-M) were found to interact with the cytoplasmic receptor tail as assayed by cross-linkage with recombinant [32P] labeled MPR 300-CT. Subcellular fractionation revealed a distinct pattern of distribution of TIP 35-M and TIP 91-M in microsomal and synaptosomal fractions. Furthermore, the formation of cross-link complexes with membrane proteins appeared to be developmentally and regionally regulated in the brain and inhibited upon ATP hydrolysis. The data suggest the requirement of specific protein interactions for MPR 300 functions in neuronal cells.

Animals

Inhibition of IGF II-induced redistribution of mannose 6-phosphate receptors by the phosphatidylinositol 3-kinase inhibitor, wortmannin.

The effects of wortmannin, a selective inhibitor of phosphatidylinositol (PI)3-kinase on insulin-like growth factor II (IGF II)-induced redistribution of the 300 kDa mannose 6-phosphate/IGF II receptor (MPR 300) has been studied in human hepatoma HepG2 cells. IGF II increased the expression of MPR 300 at the cell surface threefold that was completely abolished by wortmannin at 100-300 nM. Higher concentrations of wortmannin also reduced the basal MPR 300-dependent uptake of ligands to 68% of controls. Neither the transport of two lysosomal enzymes nor the secretion of the IGF binding protein-1 were affected by wortmannin. These results show that activation of PI3-kinase plays a critical role in the IGF II-stimulated redistribution of MPR 300 initiated rather by IGF II binding to tyrosine kinase receptors than to the MPR 300.

Androstadienes

Synthesis of insulinlike growth factor binding proteins and of the acid-labile subunit in primary cultures of rat hepatocytes, of Kupffer cells, and in cocultures: regulation by insulin, insulinlike growth factor, and growth hormone.

The adult liver is the main source of circulating insulinlike growth factors (IGFs) and their serum binding proteins (IGFBPs) including the acid-labile subunit (ALS), a component of the ternary binding protein complex. Within the liver, the biosynthesis of individual proteins has been attributed to different cell populations, e.g., that of ALS to hepatocytes and that of IGFBP-3 to nonparenchymal cells. Ligand and immunoblotting as well as Northern blotting analyses were used to study synthesis of IGFBPs and their hormonal regulation in cultured adult rat hepatocytes, Kupffer cells (KCs), and cocultures. In hepatocytes, synthesis of IGFBP-1, -2, and -4 was observed; insulin and IGF-I decreased that of IGFBP-1, and -2 while increasing that of IGFBP-4. KCs synthesized IGFBP-2, and -3, insulin and IGF-I showing no effect. In cocultures, however, synthesis of IGFBP-3 was stimulated by insulin and IGF-I. By immunocytochemistry IGFBP-3 biosynthesis was localized to KCs exclusively. When pore membranes were used for separation of hepatocytes and KCs in coculture, this insulin-stimulatory action on IGFBP-3 synthesis was preserved. Growth hormone (GH) did not affect biosynthesis of IGFBPs. Expression of ALS was localized in hepatocytes only. Insulin, IGF-I, and GH increased ALS expression. It can be concluded that biosynthesis of individual IGFBPs and of ALS are compartmentalized in adult rat liver and are distinctly regulated by insulin, IGF-I, and GH. The insulin-dependent stimulation of IGFBP-3 synthesis in KCs appears to require a diffusable mediator derived from hepatocytes.

Animals

Immunohistochemical localization of insulin-like growth factor binding protein-1, -3 and -4 in human fetal tissues and their analysis in media from fetal tissue explants.

The actions of insulin-like growth factor (IGF) II that are important in the regulation of fetal growth and development, are modulated by IGF binding proteins (IGFBPs). We have determined the cellular distribution of IGF-II and IGFBP-1, -3 and -4 in 12-week gestation human fetal tissues using immunocytochemistry. IGF-II immunostaining was found in all organs examined, with strongest immunoreactivity in spinal ganglia, tubular cells of the mesonephros and peri- and epidermal layers of the skin. The immunoreactivity distribution of all IGFBPs was similar to that of IGF-II except lung, hepatic parenchyma, fibrocytes of connective tissue and cells of the growth plate in the cartilage. When conditioned media from skin, liver, lung and kidney explants were analyzed, phosphorylated IGFBP-1 was only detected in liver samples whereas IGFBP-3 was found in all media. Weak immunoreactivity of IGFBP-4 was seen in media from lung tissue. To determine whether proteolytic degradation of IGFBPs were responsible for the different IGFBP levels, cell-free conditioned media were incubated with recombinant human IGFBPs. At neutral pH only proteolysis of IGFBP-4 was observed in media from skin and lung tissue. Upon acidification of the medium samples, IGFBP-1 fragments were formed in skin-derived medium and IGFBP-3 was cleaved by medium from lung and kidney tissue. Acid-activated proteolytic activity against IGFBP-4 was found in the media from lung and liver. These findings suggest that IGFBP proteases may be important in locally defining the concentrations of IGFBPs and contribute to tissue-specific growth response to IGFs.

Antibodies, Monoclonal

Does the overexpression of pro-insulin-like growth factor-II in transfected human embryonic kidney fibroblasts increase the secretion of lysosomal enzymes?

Insulin-like growth factor-II (IGF-II) and lysosomal enzymes bearing the mannose 6-phosphate (Man6P) recognition marker, bind to two distinct binding sites of the IGF-II/M6P receptor. The two classes of ligands reciprocally modulate the binding of the other class of ligand to the receptor [Kiess, W., Thomas, C. L., Greenstein, L., Lee, L., Sklar, M. M., Rechler, M. M., Sahagian, G. G. & Nissley, S. P. (1989) J. Biol. Chem. 264, 4710-4714]. We asked whether or not overexpression of pro-IGF-II by cells in culture leads to missorting of lysosomal enzymes. Human embryonal kidney fibroblasts were transfected with the full-length human IGF-II cDNA or a control cDNA. Solution hybridization/RNase protection experiments using a human IGF-II riboprobe showed that two transfectants expressed large quantities of IGF-II mRNA, whereas the non-transfected cells did not. The analysis of conditioned media revealed that these cells secrete approximately 0.15 micrograms and 1.0 micrograms immunoreactive IGF-II/ml and 22 x 10(6) cells and 24 x 10(6) cells within 24 hours. Immunoreactive IGF-II was shown by Western blotting to represent 17-kDa pro-IGF-II. The amount of the lysosomal enzyme, beta-hexosaminidase, was approximately twofold increased in the conditioned media from pro-IGF-II overexpressing cells compared with control media, as shown by Western-blot analysis and immunoprecipitation of media extracts of metabolically labeled cells. The synthesis rate of beta-hexosaminidase was not affected by pro-IGF-II overexpression. In addition, the basal amount of another newly synthesized lysosomal enzyme, the cathepsin D precursor, was also twofold higher in pro-IGF-II overexpressing cells than in control cells. In contrast, the surface binding and cellular uptake rate of a Man6P-containing neoglycoprotein did not differ between the cell lines. The results indicate that the overexpression of pro-IGF-II doubles the secretion and/or reduces the re-uptake of beta-hexosaminidase and cathepsin D to approximately 20% of the total synthesized enzymes in human embryonal kidney fibroblasts compared to control cells. We hypothesize that, in cells synthesizing high amounts of pro-IGF-II, the growth factor may modulate the targeting of a portion of lysosomal enzymes, mainly by partially enhancing the secretion of newly synthesized enzymes and, in addition, possibly by affecting the re-uptake mechanism.

Cathepsin D

Localization of the insulin-like growth factor II binding site to amino acids 1508-1566 in repeat 11 of the mannose 6-phosphate/insulin-like growth factor II receptor.

The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF-II receptor) binds insulin-like growth factor II (IGF-II) with high affinity. To localize the IGF-II binding site within the 15 repeating units that form the extracytoplasmic domain of the receptor, purified human M6P/IGF-II receptor was digested with thermolysin, and the fragments were analyzed for their ability to bind 125I-IGF-II in a cross-linking assay. Two IGF-II-binding receptor fragments of 23 and 37 kDa were purified. Sequence analysis revealed that the fragments consist of disulfide connected peptides comprising amino acids 1331-1566 and 1331-1697 of the receptor repeats 9-12. In a second approach we expressed truncated forms of the M6P/IGF-II receptor fused to the C terminus of the extracytoplasmic domain of the 46-kDa mannose 6-phosphate receptor. Fusion proteins containing M6P/IGF-II receptor repeats 10-15, 10-11, or 11-15 bound IGF-II, whereas a fusion protein containing the single repeat 10 failed to bind. This result indicates that repeat 11 (amino acids 1508-1650) is sufficient for binding of IGF-II. Residues 1508-1566, which are shared by the 23-kDa IGF-II-binding fragment and repeat 11, are proposed to form the IGF-II binding site of the M6P/IGF-II receptor.

Amino Acid Sequence

Mannose 6-phosphate/insulin-like growth factor II receptor fails to interact with G-proteins. Analysis of mutant cytoplasmic receptor domains.

The binding of insulin-like growth factor II (IGF II) to the mannose 6-phosphate (M6P)/IGF II receptor has previously been reported to induce the activation of trimeric G(i)2 proteins by functional coupling to a 14-amino acid region within the cytoplasmic receptor domain (Nishimoto, I., Murayama, Y., Katada, T., Ui, M., and Ogata, E. (1989) J. Biol. Chem. 264, 14029-14038). In the present study, we examined further the potential functional coupling of G-proteins with the human M6P/IGF II receptor and mutant receptors lacking the proposed G-protein activator sequence. IGF II treatment of mouse L-cells expressing either wild type or mutant M6P/IGF II receptors failed to attenuate the pertussis toxin-catalyzed modification of a 40-kDa protein or enhance GTPase activity. In broken L-cell membranes expressing wild type or mutant M6P/IGF II receptors, 30 nM IGF II also failed to affect the pertussis toxin substrate activity. By using phospholipid vesicles reconstituted with human wild type or mutant M6P/IGF II receptors and pertussis toxin-sensitive G-proteins, no stimulation of GTP gamma S binding to or GTPase activity of G(i)2, G(o)1, or G(i)/G(o) mixtures were observed in response to 1 microM IGF II. Furthermore, in vesicles containing purified wild type M6P/IGF II receptors and monomeric G alpha o1 or G alpha i2 and beta gamma dimers no effects of IGF II on GTP gamma S binding could be detected. However, when vesicles reconstituted with M6P/IGF II receptors and G(i)2 proteins were incubated with 100 microM mastoparan GTP gamma S binding was stimulated and GTPase activity was increased significantly. These results indicate that the human M6P/IGF II receptor neither interacts with G-proteins in mouse L-cell membranes nor is coupled to G(i)2 proteins in phospholipid vesicles. This study suggests strongly that the M6P/IGF II receptor does not function in transmembrane signaling in response to IGF II.

Adenosine Diphosphate Ribose

Effect of insulin-like growth factor II on uptake of arylsulfatase A by cultured rat hepatocytes and Kupffer cells.

Mannose 6-phosphate/insulin-like growth factor II receptors have been characterized in hepatocytes and Kupffer cells isolated from adult rat liver. Affinity labeling with [125I]insulin-like growth factor II revealed a protein of Mr 250,000 in both cell types. Labeling was inhibited by an antiserum against the mannose 6-phosphate/insulin-like growth factor II receptor. In Kupffer cells, [125I]insulin-like growth factor II was also cross-linked to a second protein of Mr 130,000. In both cell types, insulin-like growth factor II was 10 times more potent than insulin-like growth factor I in displacing [125I]insulin-like growth factor II from its receptor. The mannose 6-phosphate-specific uptake of [125I]arylsulfatase A via the mannose 6-phosphate/insulin-like growth factor II receptor was inhibited by insulin-like growth factor II and antibodies against the receptor, but was not affected by insulin-like growth factor I, insulin or transforming growth factor beta 1. Cell surface iodination followed by immunoprecipitation of the mannose 6-phosphate/insulin-like growth factor II receptor showed that expression of the mannose 6-phosphate/insulin-like growth factor II receptors at the plasma membrane was increased two-fold by insulin-like growth factor II. These results suggest that binding of insulin-like growth factor II to the mannose 6-phosphate/insulin-like growth factor II receptor blocks the binding and uptake of mannose 6-phosphate-containing lysosomal enzymes and may be directly involved in a co-ordinate regulation of ligand uptake from plasma into hepatocytes and Kupffer cells.

Animals

Proteolysis of IGFBPs by cathepsin D in vitro and in cathepsin D-deficient mice.

Affinity-purified lysosomal protease cathepsin D cleaved recombinant human IGFBP-1 to -5 in fragments of defined sizes, while IGFBP-6 was not degraded. To assess the role of cathepsin D for proteolytic processing of IGFBP in vivo, serum from cathepsin D-deficient mice and conditioned media from cathepsin D-deficient fibroblasts and organ explants were analyzed. No differences for the pattern and level of IGFBPs were detected. When conditioned media from fibroblasts were incubated at acid pH, proteolysis of IGFBP-1 and -4 was observed only in media derived from cathepsin D-expressing cells. Additional experiments showed that the proteolysis of IGFBP-4 is mediated by cathepsin D and not by a protease activated by cathepsin D. The IGFBP-4 degrading activities in media from organ explants from cathepsin D-deficient mice were found to be sensitive to inhibitors of aspartyl and cysteine proteases. The data indicate that different classes of acid pH-dependent proteases can contribute to the regulation of IGFBP-4 abundance.

Animals

Cellular localization and hormonal regulation of biosynthesis of insulin-like growth factor binding proteins and of the acid-labile subunit within rat liver.

In the circulation, most of the IGFs are bound to a high molecular weight binding protein complex of 150 kDa that consists of IGF-I (or IGF-II), IGFBP-3 and the acid-labile subunit (ALS). Within rat liver, individual components of the 150 kDa complex are synthesized in different cellular compartments. ALS expression is localized in hepatocytes, but not in non-parenchymal cells. IGFBP-3 mRNA, however, is exclusively expressed in non-parenchymal and among them in endothelial and Kupffer cells. Co-cultures of hepatocytes and Kupffer cells were used as a model to study the hormonal regulation of biosynthesis of the components of the 150 kDa complex. Although expressed in different liver cell populations IGFBP-3 and ALS were regulated synergistically. Insulin stimulated both the expression of ALS and IGFBP-3 in co-cultures in a dose-dependent manner, while expression of IGFBP-I was decreased. Regulation of IGFBP-3 synthesis of Kupffer cells required a mediator that is secreted by hepatocytes, since IGFBP-3 expression in cultures of pure Kupffer cells did not respond to the stimulating effect of insulin.

Animals

Regulation of insulin-like growth factor (IGF)-binding protein-6 and mannose 6-phosphate/IGF-II receptor expression in IGF-IL-overexpressing NIH 3T3 cells.

Insulin-like growth factor II (IGF-II)-overexpressing NIH 3T3 cells were used to examine regulation of insulin-like growth factor binding protein (IGFBP) and mannose 6-phosphate (M6P)/IGF-II receptor expression. Ligand blot analysis of conditioned media indicated a predominant IGFBP of 26-28 kilodaltons the abundance of which is 3- to 10-fold higher in media of IGF-II-overexpressing cells. The IGFBP level in control cell medium was increased by incubation in the presence of IGF-II, IGF-I, and mutant IGF-II forms with reduced affinities for IGF-I or M6P/IGF-II receptors. Further proof that IGF-II regulated the IGFBP was obtained by incubation of IGF-II overexpressing cells in the presence of antisense IGF-II oligomers or anti-IGF-II antibodies, which resulted in significant reduction of the IGFBP in conditioned medium. Mouse IGFBP-6 mRNA expression was increased in IGF-II-overexpressing or IGF-II-treated control cells. The IGFBP contained O-linked carbohydrate residues and was recognized by an antiserum to rat IGFBP-6. To determine whether IGFs were influencing proteolytic degradation of IGFBPs, cell-free conditioned media were incubated at 37 C with recombinant human IGFBPs. At neutral pH proteolysis of IGFBP-5 occurred during incubation in conditioned media from control and IGF-II-overexpressing cells. Upon acidification of the medium samples, only the degradation of IGFBP-6 was prevented in IGF-II-overexpressing cell-conditioned medium.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells

In vitro phosphorylation of the 46-kDa mannose 6-phosphate receptor by casein kinase II. Structural requirements for efficient phosphorylation.

Some steps in the receptor-mediated transport of newly synthesized mannose 6-phosphate-containing lysosomal enzymes are assumed to be accompanied by changes in the phosphorylation state of receptors. In vitro, the metabolically phosphorylated 46-kDa mannose 6-phosphate receptor (MPR 46) was dephosphorylated by protein phosphatase 2A. The synthetic cytoplasmic domain of MPR 46 was phosphorylated in vitro by casein kinase II. Tryptic phosphopeptide mapping showed that casein kinase II phosphorylates MPR 46 in vitro at the same site that is phosphorylated in vivo. Inhibition studies using synthetic peptides corresponding to different amino acid sequences of the cytoplasmic tail of MPR 46 revealed that the sequence 26-32 (ADGCDFV) contribute to efficient phosphorylation of serine 56. Baby hamster kidney cells were transfected with wild type human MPR 46 cDNA or cDNAs containing mutations in the cytoplasmic tail and assayed for their phosphorylation state in vivo. The phosphorylation of mutant receptors with deleted residues 23-28 (NLVADG) was strongly reduced. These data indicate that residues on the N-terminal side of the phosphorylatable serine 56 may influence the efficiency with which a casein-kinase II-like kinase phosphorylates MPR 46.

Amino Acid Sequence

Specific mannose-6-phosphate receptor-independent sorting of pro-cathepsin D in breast cancer cells.

The secretion of pro-cathepsin D (pro-cath-D) in some human metastatic breast cancer cells (MCF7, MDA/MB231), contrary to normal mammary cells, is not increased by ammonium chloride treatment, indicating a mannose-6-phosphate-independent sorting to lysosomes. By studying a variety of cell lines and lysosomal enzymes, we show that secretion of newly synthesized pro-cath-D was not mediated by the 46-kDa mannose-6-phosphate receptor (MPR) and that its resistance to NH4Cl for secretion was specific to cath-D and not to other lysosomal enzymes. This resistance appeared to be correlated with the basal hypersecretion of pro-cath-D, but not with its overexpression. By contrast, pro-cath-D secretion was increased by NH4Cl in fibroblasts and nontumoral epithelial mammary cells, suggesting a specificity for cancer cells. Immunofluorescence staining showed that pro-cath-D, but neither cathepsin B nor beta-hexosaminidase, accumulated in intracytoplasmic vesicles of cells treated with ammonium chloride. In pulse--chase experiments and by subcellular fractionation on Percoll gradient, cath-D was found to be sorted into dense lysosomes whether cells were treated or not by NH4Cl. Treatment of cells with NH4Cl, however, inhibited processing and maturation of pro-cath-D, which was also observed in light vesicles in the absence of NH4Cl. Part of pro-cath-D, but not processed enzyme, was also found to be membrane associated in saponin-permeabilized cells. We conclude that in breast cancer cells, the MPR-independent pathway of pro-cath-D to lysosome is predominant compared to normal cells and other lysosomal enzymes. This alternative pathway should therefore be considered, in addition to MPR, to explain pro-cath-D sorting and activation in breast cancer cells.

Ammonium Chloride

Effects of insulin-like growth factor II on the generation of inositol trisphosphate, diacylglycerol and cAMP in human fibroblasts.

In human fibroblasts, exogenous insulin-like growth factor-II (IGF-II) induce a rapid redistribution of mannose 6-phosphate/IGF-II receptors. To analyze the mechanism transducing the IGF-II signal the phosphoinositide hydrolysis, 1,2-diacyglycerol and cAMP formation were studied after incubation with IGFs. While IGF-I (10 nM, 30 s) increased the inositol trisphosphate formation IGF-II (10 nM, up to 10 min) failed to affect phosphoinositide hydrolysis and had neither an effect on basal concentrations of diacylglycerol containing arachidonic acid or myristic acid nor on intracellular cAMP. On the contrary, pretreatment with IGF-II for 10 min enhanced the cAMP production stimulated by bradykinin (10 nM, 3 min) by 2.5-fold whereas no additive effects of IGF-II on the increased ligand binding to the mannose 6-phosphate/IGF-II receptor in response to bradykinin were observed. These results indicate that in fibroblasts the rapid IGF-II-induced redistribution of mannose 6-phosphate/IGF-II receptors is not mediated by inositol trisphosphate, diacylglycerol or cAMP, but that IGF-II may modulate permissively other agonist-generated signals.

Arachidonic Acid

Proteolysis of insulin-like growth factor binding protein-5 by pregnancy serum and amniotic fluid.

Incubation of iodinated recombinant human insulin-like growth factor binding protein (rhIGFBP)-5 with pregnancy serum or amniotic fluid resulted in the formation of 22- and 15 kDa fragments. Non-pregnancy serum did not contain IGFBP-5 proteolytic activity. Size fractionation revealed the proteolytic activity both in serum and amniotic fluid in a > 100 kDa fraction which co-eluted in gel filtration with proteins of approx. 200 kDa. The IGFBP-5 protease activity was inhibited by EDTA, phenanthroline and PMSF. The formation of proteolytic fragments was also observed using 125I labeled rhIGFBP-3 and -4 but not with rhIGFBP-1 or -6 as substrate. The data demonstrate that pregnancy serum and amniotic fluid contain a very similar cation-dependent serine protease which degrades IGFBP-3, -4 and -5.

Amniotic Fluid

Transport of newly synthesized arylsulfatase A to the lysosome via transferrin receptor-positive compartments.

We have studied the convergence of the biosynthetic lysosomal route marked by the newly synthesized lysosomal enzyme arylsulfatase A (ASA) with the endosomal/prelysosomal compartment in ASA overexpressing baby hamster kidney (BHK) cells. A monoclonal antibody against ASA conjugated to transferrin (Tf-alpha ASA) was used to load the endocytic pathway via the transferrin receptor. Subsequent internalization of [125I]labeled ASA and Tf-alpha ASA conjugates at 18 degrees C followed by rewarming to 37 degrees C showed that immunocomplexes were formed within the recycling pathway and released into the medium. Furthermore, in cells labeled with [35S]methionine for 10 min about 54% of newly synthesized ASA passed into Tf-alpha ASA accessible compartments during a 4 hour chase period and accumulated in the medium. These data indicate that in overexpressing BHK cells the majority of newly synthesized ASA is transported to the lysosome via transferrin receptor-containing early endosomes.

Animals

Phosphorylation of the cytoplasmic tail of the 300-kDa mannose 6-phosphate receptor is required for the interaction with a cytosolic protein.

The cytoplasmic tail of the human 300-kDa mannose 6-phosphate receptor (MPR 300-CT) is an excellent substrate for casein kinase II in vitro. The phosphorylated MPR 300-CT was cross-linked by means of bis(sulfosuccinimidyl)suberate mainly to a cytosolic protein of 35 kDa (referred to as TIP 35) and to 35- and 91-kDa proteins salt-washed from bovine brain membranes. Gel filtration suggested that TIP 35 is part of a higher molecular mass complex of approximately 130-150 kDa. Inhibition studies, using non-phosphorylated and phosphorylated MPR 300-CT and cross-linking, indicate that the interaction with TIP 35 is phosphorylation-specific. Furthermore, TIP 35 was only cross-linked to the MPR 300-CT phosphorylated by casein kinase II whereas the MPR 300-CT phosphorylated by protein kinase A failed to cross-link to TIP 35. These results indicate that the cytoplasmic tail of the MPR 300 interacts with a cytosolic protein depending on the phosphorylation by a casein kinase II-like kinase. The cross-linking with salt-washed membrane proteins, however, is inhibited by non-phosphorylated MPR 300-CT, suggesting that different structural determinants in the MPR 300-CT interact with cytosol- and membrane-derived proteins.

Animals